In the electronic paper terminal, the pen input type portable electronic computer, and the portable game device, it is popular to be configured in such a way that the display section occupies most of the front side of the device, and is surrounded all around by a housing (such a device is called “portable display device” herein). Recent portable display devices have been designed to have higher definition and larger display sections regardless of the display type, such as liquid crystal, organic electroluminescence or electrophoresis.
In such a portable display, the center of gravity is positioned near the center portion where the display section is located, so that a load may be applied to hands holding the device depending on the position of an operation section or a holding section provided at the housing. In this respect, there is known a pen input type portable electronic computer which is configured to have command input keys provided on the upper surface of the device at a good operational position or good holding position according to the shape of the device, the weight thereof, the position of the center of gravity, and the use.
There is known a device for fire alarm equipment, though not a portable display device, which is configured to have an operation section, such as switches, provided on the hand side of the housing that constitutes the device, a battery box disposed near the operation section in the housing, and the center of gravity positioned on the hand side of the housing.
With regard to the former pen input type portable electronic computer mentioned above, it is proposed to provide command input keys at a good operational position or good holding position according to the position of the center of the device. However, in the common portable display device, the housing weighs about 30 percent of the total weight of the portable display device, and the chassis of the display section weighs another 30 percent or so. Since the housing and chassis are governing the center of gravity of a portable display device, the center of gravity of a general portable display device is located near the center portion of the device. Accordingly, the “good operational position” and the “good holding position” are actually determined specifically based on the center of gravity, thereby raising a problem that there is no flexibility for the mounting position of the operation section or the holding section.
Even if the former pen input type portable electronic computer has the command input keys provided in a good operational position or good holding position, it still has a problem that the load (moment) to be applied to a device holding hand (a hand which holds the device) cannot be reduced at all since the device is configured in such a way that one side portion apart from the position of the center of gravity of the device is held.
In this respect, the latter device for fire alarm equipment shifts the position of the center of gravity of the device toward the operation section using the weight of the battery set in the battery box. Since the housing and chassis of an ordinary portable display device occupy about 60 percent of the total weight, however, merely shifting the installation position of the battery which, together with the display section or other parts, is included in the remaining 40 percent does not have a large influence on the position of the center of gravity of the device.